Insects have plagued people throughout history. Fast intercontinental travel and trade have enabled the importation of nonindigenous insect pests (e.g., species of mosquitoes, such as Aedes albopictus, the Asian Tiger mosquito) into the United States. As a result, the U.S. must face the task of controlling numerous species of nuisance pests, such as arthropods and, more specifically, mosquitoes. Some of these insects spread disease and, thus, are of great medical and veterinary importance. Control of these pests is necessary to reduce or eliminate the spread of arthropod-borne diseases.
The primary focus of this invention is the control or reduction of the population of mosquitoes. At least three "generations" of control methods have been developed over the years. The first generation of control methods comprise chemicals dispensed by foggers or sprayers, both on the ground and through the air. These chemicals may be classified as either adulticides or larvicides and are intended to attack and kill the adult mosquito or its larva, respectively. These chemicals usually have an inherent toxicity, which is potentially injurious to the environment, to marine life and wildlife, and ultimately to humans. As a result, these chemical insecticides have become viewed with disfavor.
One such insecticide product was "DURSBAN.TM. 10CR" produced by Dow Chemical Company in the mid-1970's. There were at least two problems with this product. First, it was inherently toxic and potentially harmful to the environment. Second, because of rapid turnover of the mosquito population and the selection of resistant genes by Dursban, insects could develop a resistance to the chemicals. Mosquitoes ultimately develop an immunity to adulticides of the same chemical family. This situation is referred to as "cross resistance" and illustrates that under adverse conditions, insects may adapt. This ability to adapt, often within a few generations, provides complications for researchers engaged in the field of pest control.
As a departure from the chemical adulticides and larvicides, a second generation of mosquito control product was developed. This second generation is known as insect growth regulators. Their purpose is to prevent the immature insect from transforming into an adult. This class of mosquito control product allows the larva to enter into its pupa stage but prevent the pupa from developing into an adult. These products have very low toxicity, or practically no toxicity, and hence are not detrimental to aquatic life. Due to the general application of this control material to the environment through a form such as a charcoal briquet, the products are messy, inconvenient to handle, and are very expensive. These products also require adequate surveillance of standing water and delivery of briquets to these locations. The potential exists that some sites will go untreated.
Over the past fifteen years, a third generation of insecticides has been developed. These are bacteriological methods for spreading endotoxins among insect populations. One of the most successful endotoxin agents used against insects is Bacillus thuringiensis Berliner var. kurstaki, a bacterium which infects the larvae of Lepidoptera (moths) that are to be destroyed. More recently, a new variety has been uncovered for use against mosquito and black fly larvae. This is Bacillus thuringiensis Berliner var. israelensis and its accompanying proteinaceous parasporal particles which contain protoxin. When a larvicidal microorganism of the bacillus type is used and is sprayed on the water in the form of a liquid produced by diluting the wettable powder or liquid concentrate with water, a similar problem is encountered. The bacillus spores and protoxin particles are heavier than water and sink. Additionally, the application of the bacillus does not have a sustained release--it is essentially "one shot"--and hence re-applications are often necessary to insure an effective mosquito control program. This is time consuming and expensive, and extensive surveillance is needed to target all breeding areas.
Besides these existing chemical and microbial insecticides, other devices and methods are known for the control or destruction of mosquitos and other aquatic pests.
U.S. Pat. Nos. 4,166,112 and 4,187,200, issued to Goldberg in 1979 and 1980, respectively, disclosed Bacillus thuringiensis in which a carrier was formulated as a buoyant colloidal suspension which stabilized just under the surface of the water.
According to information published by Biochem Products, a division of Salsbury Laboratories, Inc., a member of the Solvay Group, the earliest documented record of Bacillus thuringiensis was in Japan in 1901. In the decades since, at least 14 varieties of B.t have been identified from several countries on the bases of biochemical characteristics and serotyping of vegetative cell flagellar antigens. Bacillus thuringiensis, Berliner also known as HD-1, Serotype H-3a3b, or B.t. variety kurstaki, has been registered in the United States since 1961 for control of Lepidopteran larvae or caterpillars and is the type commonly used in forestry, agriculture, home and commercial gardening and horticulture. Products containing B.t reportedly have an excellent safety record with no documented incidents of serious or undesirable side effects on man and the environment. Biochem Products supplies a wettable powder or a flowable concentrate under the trademark "BACTIMOS.TM." which is derived from B.t.i., Serotype H-14, Bacillus thuringiensis variety israelensis, and was discovered in Israel in 1976. This is a larvicidal microorganism comprising Bacillus thuringiensis Berliner var. israelensis and its accompanying proteinaceous parasporal particles which contain protoxin (commonly referred to as "B.t.i.").
For mosquito control purposes, the BACTIMOS.TM. (B.t.i.) is invariably mixed with water and is applied to large areas, using airplanes or helicopters. This method of application has been continually used despite the constant and critical need for an alternate delivery system for the myriad of ponds and other small bodies of water, as recognized in MOSQUITO NEWS in 1948.
Moreover, any attempt to impregnate B.t.i. (or the larvicidal microorganism of the aforesaid Goldberg patents) into the floating thermoplastic carrier of the aforesaid Cardarelli patent, would be impractical (if not impossible) and would destroy the stated utility of these references. An exposure of the B.t.i. particles to temperatures above 70.degree. or 80.degree. Celsius depending upon the exposure time, which is inversely correlated with temperature--will cause the B.t.i. to suffer a protein denaturization, resulting in a change in its molecular structure and a loss of its activity. Thus, it would be impractical to attempt to incorporate B.t.i. into a thermoplastic or elastomeric strip of material, in view of the molding temperatures likely to be encountered. Moreover, even if the B.t.i. could be incorporated into a polymer or elastomeric matrix without substantially limiting or destroying its efficacy, these B.t.i. particles are agglomerations of relatively large molecules and are incapable of migrating within a polymer or elastomeric matrix. Hence, they would not even be released, since the active protein toxin has a molecular weight of approximately 28 megadaltons. The aforementioned methods are efficient, but are performed at high monetary costs to mosquito districts and taxpayers. Ultimately, the mosquitoes sought to be controlled are those noticed readily by humans, i.e. mosquitoes and blood-sucking flies that draw blood meals from humans.
Thus, numerous severe problems exist with the mosquito extermination methods that use chemical insecticides. As such, an alternative approach toward arthropod surveillance and control has been developed. One such promising method is the use of chemicals as attractants for mosquitoes and other arthropods that prey on human and animal hosts. The combination of highly effective chemical attractants with efficient traps allows for a control method to be developed similar to that used to control the Tsetse fly in Africa (Vale and Hall, Bull. Ent. Res., 75, 219-231 (1985)). Because effective attractants are known for the Tsetse fly, a control method using only baited traps was developed and is very effective.
Current surveillance techniques rely on light traps or other traps which are relatively inefficient in mosquito collection. Sentinel chickens are used to assess transmission risk of encephalitis to humans in a local area. Better traps via more efficient and less expensive lures or baits would greatly aid in this endeavor. One example of a trap, U.S. Pat. No. 5,657,756 to Nicosia, 1997, involves collection and trapping of arthropods using warmed circulated fluid.
Carbon dioxide has been shown to attract mosquitoes. Willis, J. Exp. Zool, 121, 149-179 (1952), discloses that Aedes aegypti (mosquitoes) are attracted to carbon dioxide. From amputation experiments on female Aedes aegypti, it was discovered that carbon dioxide receptors were located on the antennae. The role of carbon dioxide in the attraction of mosquitoes to hosts also has been the subject of numerous laboratory studies. Rudolfs, N. J. Agric. Exp. Sta. Bull., 367 (1922), and Gouck, J. Econ. Entomol., 55, 386-392 (1962), describe carbon dioxide as an activator, rather than an actual attractant.
Acree, Science, 1346-7 (1968), discloses that L-lactic acid, isolated from the human hand, attracts female Aedes aegypti. It also discloses that carbon dioxide is necessary to observe this attraction.
Wensler, Can. J. Zool., 50, 415-420 (1972), discloses the use of ethyl ether soluble honey odors to attract Ae. aegypti.
Compositions consisting of lactic acid analogues and carbon dioxide have also been shown to attract mosquitoes. Carlson, J. Econ. Entomol., 66, 329-331 (1973), discloses that some tested analogues of lactic acid had equivalent attraction to L-lactic acid, but this was not true at all tested doses. The highest reported attraction was 40% of female Ae. aegypti.
Bar-Zeev, J. Med. Entomol., 14, 113-20 (1977), discloses that a composition consisting solely of lactic acid and carbon dioxide attracts Ae. aegypti. Here, the lactic acid was dissolved in acetone, similar to the use of methanol for the invention described in this application. It is clearly stated that the acetone solvent was evaporated from the filter paper prior to the carbon dioxide being allowed to pass into the flask. Acetone was chosen for its properties as a solvent, i.e., good ability to dissolve L-lactic acid and high volatility resulting in rapid evaporation or drying.
Price, J. Chem. Ecol., 5, 383-95 (1979), discloses that human emanations and carbon dioxide attract female An. quadrimaculatus.
Lactic acid was shown to attract mosquitoes such as virgin Ae. aegypti (mosquitoes) by Davis, J. Insect Physiol., 30, 211-15 (1984).
Gillies, Bull. Entomol. Res., 70, 525-32 (1980), reviews the use of carbon dioxide to activate and attract mosquitoes.
Schreck, J. Chem. Ecol., 8, 429-38 (1981), discloses that materials isolated from human hands, other than L-lactic acid, attract female Ae. aegypti and An. quadrimaculatus mosquitoes.
Lactic acid, in combination with phosphorous-containing compounds have been shown to attract mosquitoes. Ikeshoji, Jpn. J. Sanit. Zool., 38, 333-38 (1987), discloses lactic acid and hempa; lactic acid and metepa; lactic acid, metepa and olive oil; and lactic acid and DDVP attract mosquitoes.
Lactic acid-related compounds have also been tested as mosquito attractants by electrophysiology. Davis, J. Insect Physiol., 34, 443-49 (1988), discloses that neurons in the antennae are excited by L-lactic acid, and that analogues of lactic acid, e.g., carboxylic acids, alcohols, hydroxyacids, aldehydes, thiols and haloacids were tested for neuron response. It was shown that no compound elicited as high of a relative responsiveness toward lactic acid-excited cells as did lactic itself.
It has been shown that carbon dioxide, in combination with other chemicals, serves as an attractant for mosquitoes. Takken and Kline, J. Am. Mosq. Control Assoc., 5, 311-6 (1989), disclose 1-octen-3-ol (octenol) and carbon dioxide as mosquito attractants. Van Essen, Med. Vet. Entomol., 63-7 (1993), discloses the use of carbon dioxide, octenol, and light to attract several species of mosquitoes. Takken, J. Insect Behavior, 10, 395-407 (1997), discloses that a composition consisting solely of carbon dioxide, acetone and octenol attracts several species of mosquitoes.
Kline, Med. Vet. Entomol., 4, 383-91 (1990), discloses that honey extract, octenol, carbon dioxide, L-lactic acid plus carbon dioxide, L-lactic acid plus octenol plus carbon dioxide attract mosquitoes well and butanone plus carbon dioxide, and phenol alone are less effective.
Schreck, J. Am. Mosq, Control Assoc., 6, 406-10 (1990), discloses that materials isolated from human skin attract female Ae. aegypti and An. quadrimaculatus (mosquitoes), and the level of attraction, transferred to glass, varies from person to person. It also discloses that differences in attraction level are present depending on the body location origin of the material.
Takken, Insect Sci. Applic., 12, 287-95 (1991), reviews mosquito attractants and lists acids, alone or in combination with other amino acids that are attractive for mosquitoes.
Eiras, Bull. Entomol. Res., 81, 151-60 (1991), discloses that lactic acid, carbon dioxide, human sweat and thermal convection currents attract female Ae. aegypti.
Carlson, J. Med. Entomol., 29, 165-70 (1992), discloses that the release of carbon dioxide from the human hand is negligible and therefore is not a factor in the attraction of Ae. aegypti (mosquitoes) to the human hand.
Bowen, J. Insect Physiol., 40, 611-15 (1994), discloses that lactic acid sensitive receptors are present in Ae. atropalpus.
Eiras, Bull. Entomol. Res., 81, 207-11 (1994), discloses that lactic acid in combination with carbon dioxide has been shown to attract mosquitoes.
Charlwood, Ann. Trop. Med. Parasitol., 89, 327-9 (1995), discloses the mosquito-mediated attraction of female mosquitoes to hosts. Several species of mosquitoes were more attracted to a host, e.g., human leg, which already had mosquitoes feeding than a host which had no mosquitoes feeding on the host (termed "invitation effect"). An apparent pheromone, which was given off by the feeding mosquitoes, was speculated to attract other mosquitoes to the host.
DeJong and Knols, Experientia, 51, 80-4 (1995), discloses that different malaria mosquito species (An. gambiae s.s. and An. atroparvus) prefer different biting sites on the human body. DeJong and Knols, Acta Tropica, 59, 333-5 (1995), disclose that An. gambiae is attracted to carbon dioxide.
Bernier, Ph.D. Dissertation, University of Florida (1995), discloses the presence of lactic acid, glycerol, and long chain acids and alcohols on the skin, as well as other chemicals for a total of over 300 compounds. Some of these were identified and examined as candidate attractants.
Geier, in Olfaction in Mosquito-Host Interactions, 132-47 (1996), discloses that carbon dioxide alone is an attractant and that lactic acid alone is a mild attractant, but that the two act as a synergistic attractant. It also discloses that fractions of ethanol washings from human skin are attractive.
Knols and DeJong, Parasitol Today, 12, 159-61 (1996), disclose that carbon dioxide in combination with Limburger cheese, serves as an attractant for female An. gambiae. It was suggested that mosquitoes are attracted to odors emanating from feet and ankles and this odor resembles Limburger cheese. It was also suggested that the odor of Limburger cheese was due to bacteria involved in cheese production which originate in human skin; cornyeform bacteria, in particular strains of Brevibacterium linens, which is closely related to Br. epidermidis, which forms part of the normal microflora of human feet, methanethiol, a pungent sulfur compound which is metabolized from L-methionine liberated during proteolytic activity and reported to contribute substantially to both cheese and foot odor; or the significant quantities of short-chained fatty acids in Limburger cheese.
McCall, J. Med. Entomol., 33, 177-9 (1996), discloses that Ae. aegypti (mosquitoes) were attracted to volatile constituents of mouse odor, but did not identify potential chemicals.
Knols, Bull. Entomol. Res., 87, 151-9 (1997), discloses the use of Limburger cheese (the acid and non-acid solvent extracted fractions) to attract An. gambiae (mosquitoes). Nineteen saturated and unsaturated aliphatic fatty acids, ranging in carbon chain lengths from C.sub.2 -C.sub.18 were identified in Limburger cheese.
Mboera, J. Vector Ecol., 23, 107-13 (1998), disclosed that Culex quinquefasciatus is attracted to a worn stocking and that carbon dioxide plus body odor did not increase response.
Kline, J.Vector. Ecol., 23, 186-94 (1998), disclosed that in olfactometer tests, the human hand or worn sock attracted 80% and 66%, respecively, of Ae. aegypti in the cage. In comparison, Limburger cheese attracted 6.4%, and the control 0.0% in the olfactometer.
Bernier, Anal, Chem., 71, 1-7 (1999), discloses the method for analysis of skin emanations, including the identification of lactic acid, glycerol, C.sub.12 -C.sub.18 carboxylic acids and C.sub.4 -C.sub.11 aldehydes.
Takken and Knots, Annu. Rev. Entomol., 44, 131-57 (1999), reviewed odor-mediated behavior of afrotropical mosquitoes, reaffirming carbon dioxide as the best known mosquito kairomone.
Braks and Takken, J. Chem. Ecol., 25, 663-72 (1999), disclose that 2-day-old incubated sweat became attractive to An. gambiae.
Various chemicals have been disclosed as attractants for mosquitoes. U.S. Pat. No. 4,818,526 to Wilson discloses the use of dimethyl disulfide and dibutyl succinate and combinations thereof as attractants for Culicidae (mosquitoes).
U.S. Pat. No. 4,907,366 to Balfour (1990) discloses the use of a composition consisting solely of lactic acid, carbon dioxide, water, and heat to attract mosquitoes.
PCT WO 98/26661 to Justus discloses mixtures of L-lactic acid and its sodium salt, glycerol, and cheese extracts, with and without unsaturated long chain carboxylic acids, alcohols and an amide as attractive for Ae. aegypti. The glycerol, as well as other components described as equivalent to the glycerol, appear to make the composition substantive, so that it does not evaporate immediately in a rapid pulse. However, the active ingredients from Limburger cheese, which are the attractant chemicals, are not disclosed within the document, nor were statistical data reported for the results used in the examples.
Several of the above-mentioned chemicals and chemical compositions have been employed to attract any of the hundreds of species of mosquitoes and related arthropods that utilize humans and animals as their hosts. In fact, many of the disclosed compositions have been claimed to be active as attractants for mosquitoes. The activities of these attractants are often inconsistent and below 50% attraction response in laboratory experiments. More specifically, none of the disclosed compositions have been able to attract mosquitoes on a consistent basis as efficiently as, or more efficiently than the human body. As such, the human body has been examined repeatedly to provide clues regarding the chemical compositions disclosed. Thus, while chemicals and chemical compositions may have been active in attracting mosquitoes, none have been classified as successful for mosquito attraction as those reported in this document.
A long-felt need therefore exists for chemical compositions that can be employed safely in the environment, and that exhibit a synergistic effect for attracting mosquitoes wherein the compositions are more efficient than the human body in attracting mosquitoes. The present invention satisfies this need. Current mosquito traps often use carbon dioxide, which in prior art was needed for efficient collection and surveillance. The present invention obviates the need for large carbon dioxide gas cylinders or dry ice by providing mosquito attractants that perform as well as, and more efficiently in place of, carbon dioxide. Although carbon dioxide is not necessary, it can still be included to release blends, as some insects may be attracted only with its inclusion.